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Re: A2B Metro restoration / modification - Fechter's first Ebike

Posted: May 08 2018 3:22pm
by JanComputerman
NOW The big concern is how far out of balance are all the cells and how well does the bms limit over voltage on a per cell group for the ten groups? May have to slow charge it for a while with something other than the four amp charger.
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Re: A2B Metro restoration / modification - Fechter's first Ebike

Posted: May 08 2018 3:27pm
by Ianhill
Hats of too you getting that hub open and back together what a nightmare.
Tap on back for sorting it go have some well deserved fun.
Give it a slow charge for 12 hours or so and the bms will do the balancing for you just keep it plugged in on slow charge make sure your green light voltage is at the correct overall pack voltage and leave it balance away for a few hour's.

Re: A2B Metro restoration / modification - Fechter's first Ebike

Posted: May 09 2018 8:25am
by fechter
Just curious exactly where you attached the charger wires when you were reviving it?

The balancing shunts on the BMS are fairly wimpy. I don't remember what current they run at, but I can check when I get home. If you can charge with a supply that is current limited to less than what the shunts take, you can run it like that for a long time to get the pack balanced. It's in the range of 50mA to 100mA. A seriously out of balance pack is going to take days to balance at 50mA.

As far as I know, the balancing shunts come on at 4.2v. HVC will cut charge off around 4.25v. If the charger is limiting to less then the shunt current, the HVC should never activate.

With just the stock charger, I'm not sure how it behaves when the pack is full. Some chargers will go green and cut off the charge current. Some will keep voltage present. If all you have is the stock charger and you want it to keep going, one trick is to place a load on the output so the current never gets down to the cutoff point. Somewhere in the ballpark of 100mA will keep it going. That light bulb might work.

I had a large supply of used Li-ion packs that were drained to zero by the BMS. These were little 2s-3p packs for equipment. They sat at zero for years. All of them that I revived seemed to return to their original capacity and have worked well. It seems if the cells are drained very slowly, it does not damage them. Same goes for the revival charge. I have had other cells what were very low (and I didn't know about it) that were permanently damaged by charging at full current.

Re: A2B Metro restoration / modification - Fechter's first Ebike

Posted: May 10 2018 8:30am
by fechter
I looked at a A2B BMS board and the shunt resistors are 100 ohms, which means the balance shunts will be running 42mA.

Re: A2B Metro restoration / modification - Fechter's first Ebike

Posted: May 11 2018 10:44pm
by Raisedeyebrows
So if you just plug a 120v 20w bulb into the output plug it will fool the BMS into balancing? Any do and don't on this for Idiot me to avoid when doing this? Thanks.

Re: A2B Metro restoration / modification - Fechter's first Ebike

Posted: May 11 2018 11:50pm
by fechter
I have never tried this, so I don't know how the charger behaves. It may take a slightly larger bulb since it's only getting 42v. It may not need the bulb at all and work by itself.

Re: A2B Metro restoration / modification - Fechter's first Ebike

Posted: May 14 2018 6:38pm
by Metro_E-cart
Nice work Fechter. I still love my 2012 Metro. I got an empty auxiliary battery case and built my own 11S8P battery pack into it a few years ago. My potted frame controller doesn't like more than 50V, so 11S is the max I can feed it. It's working fairly well. Eventually the original frame battery crapped out on me. I finally conquered the hairball and and rebuilt it with LG MJ1 cells.
Somewhere along the way I seem to have killed the BMS. There is a short on the BMS output terminals. I don't have enough electronics knowledge to figure out the defective part and switch it out. :(
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Any idea where to get a replacement BMS?

Since the MJ1 cells have 10A max discharge current I am thinking of using a Grin Phaserunner controller and hopefully fit it inside the frame.
I would still want to limit the max current to 35 or 40 amp. (That's 6.66 A per cell for the frame pack). Does anyone have experience with this kind of setup?

Re: A2B Metro restoration / modification - Fechter's first Ebike

Posted: May 14 2018 6:40pm
by Alan B
PhaseRunner's are great, and very adjustable. Good luck with your upgrade.

Re: A2B Metro restoration / modification - Fechter's first Ebike

Posted: May 14 2018 7:11pm
by fechter
Pretty much any generic 10s Chinese BMS should work. The stock one trips around 30A. I'm not sure where all the wires on the stock one are going, but on the newer ones they feed the battery meter, so you would lose this function. A separate voltmeter or CA would be better anyway.

Re: A2B Metro restoration / modification - Fechter's first Ebike

Posted: May 15 2018 11:43am
by Ianhill
The stock pack is made of sanyo ncr cells Ive been balancing external and watching total pack discharge as ncr is a fairly safe 18560 chemistry.
I found that I can use 40 battery amps discharge until I have 50% usable capacity left then I get voltage sag so I back off to 25amps to use the remaining capacity.

I've only done just over 100 miles in total, If I peddle along I can get 30 miles to the stock pack with my setup riding it just like a bike and throttleing when I need help working as a team around the 20mph mark.

Today I picked up my first victim, a drop handle in the lycra thought he could out peddle a silly cargo bike ;) I kept it just around 20mph and peddled along can't even hear it's electric like this it's so silent, after 3 miles of keeping him on the fishing line working him he was so tired he was red in face shouted at me oi mate wtf is that, haha I dropped back to talk and he was f ₩+×ed panting talk and I was fresh as explained my ride brief and powered down some more to complete a 30 mile ride.

Re: A2B Metro restoration / modification - Fechter's first Ebike

Posted: May 21 2018 2:26pm
by JanComputerman
Sorry guys been off line for a while... The stock charger runs at like 4 amps and when it reaches 42 volts or so and the current starts to drop a little it goes green and disconnects so not much time balancing. I opened up the three pin charge connector and tapped into the red and black wires outside the bike on the charger cord. Works just fine for monitoring the voltage yeah new cells so hopefully they stayed well balanced after being run way down ... Time will tell ... Have not been back to check on it yet... belongs to a client friend but told her to ride it and charge it after she puts some miles on it and runs it down a bit ...maybe keep it away from full charge for a while until I get a chance to check it and slow charge it near full like you say...bring it up to full slowly until it has a chance to balance the cells.

Re: A2B Metro restoration / modification - Fechter's first Ebike

Posted: Jul 04 2018 12:21pm
by shinyballs
Update on the dimmer I posted a few months ago, it works at 12V and 20V. Dimming is tricky to adjust, takes about 2-4 seconds to dim/brighten and I was able to use only 2 brightness settings. When connected to 3 led headlights at 20V, power output is:
Dim - 9W
Full - 28W
Since the amp draw is low at 20V, will just wire it directly to a 3-way motorcycle light switch on my scooter.